1. Field of the Invention
This invention relates to the improvement of the long-term color stability of jet fuel by removing nitrogen compounds by contacting the jet fuel with concentrated sulfuric acid.
2. Background Art
Jet fuel is used in military and non-military aircraft as a fuel. This fuel is widely used and is commonly sold in accordance with military specifications. Jet fuel is used in such quantities that it is a major product of many refineries. Jet fuel generally comprises a mixture of aromatic, olefinic and paraffinic compounds typically having a boiling range from about 350.degree. F. to about 590.degree. F. Typically, about twenty-four percent (24%) of the fuel comprises aromatic compounds, about five percent (5%) of the fuel comprises olefinic compounds and the balance comprises paraffinic compounds. Jet fuel can be produced from a variety of refinery streams but is most frequently produced from streams resulting from crude oil fractionation, and hydrocracking processes such as fixed bed catalytic hydrocracking and the like. Other sources of jet fuel constitute any suitable boiling range stream in the refinery which otherwise meets the requirements for jet fuel. One such stream is the jet fuel boiling range fractionator product from a petroleum coking operation. These fuels tend to be higher in sulfur and nitrogen than the straight run jet fuel fractions or the hydrocracker jet fuel fractions. Nonetheless, they constitute a valuable hydrocarbon product and after suitable desulfurization have been used frequently as a component of jet fuel blends.
Jet fuels meeting military specifications have been observed in recent years in some instances to develop undesirable color upon standing. While these jet fuels met all applicable specifications initially, the color develops upon storage for extended periods of time. At least one customer has developed a test for long-term color stability and has expressed interest in requiring that jet fuels have long-term color stability.
Accordingly, it would be highly desirable if jet fuels and jet fuel blends could be treated to produce desirable long-term color stability.